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THE POPULAR SCIENCE MONTHLY. 



" Think now," says Lodge, " of a cloud and of the earth under 

 it as forming the two coats of a Leyden jar, in the dielectric of 

 which houses and people exist ; we now 

 have to consider what determines a dis- 

 charge, and what happens when a dis- 

 charge occurs. The maximum tension 

 which air can stand is one half gramme 

 weight per square centimetre. At what- 

 ever point the electric tension rises to this 

 value, smash goes the air. The breakage 

 need not amount to a flash, it must give 

 way along a great length to cause a flash ; 

 if the break is only local, nothing more 

 than a brush or fizz need be seen. But 

 g when a flash does occur it must be the 

 = weakest spot which gives way first the 

 I place of maximum tension and this is 

 <i commonly on the smallest knob or surface 

 = which rears itself into the space between 

 -* the dielectrics. If there be a number of 



O 



3 small knobs or points, the glows and brushes 

 become so numerous that the tension is 

 g greatly relieved and the whole of a mod- 

 ^ erate thunder-cloud might be discharged 

 s in this way without the least violence. . . . 

 But sometimes a flash will descend so quick- 

 a ly or it will have such a tremendous store 

 of energy to get rid of that no points are 

 I sufficiently rapid for the work, and crash it 

 all comes at once. One specially note- 

 s' worthy case is when one cloud sparks into 

 ^ another and thence to the ground; or in 

 | general whenever electric strain is thrown 

 k>^ quite suddenly upon a layer of air." 



Thus, then, we begin to see that much 

 ^ ^ will depend upon the character of the flash. 

 | * There are many flashes, I believe, that the 

 ^ body could experience without very seri- 



ous consequences ; and there are many 

 ^ that will rive solid granite and shatter in 



s splinters the heaviest masonry. The im- 



^ pulsive rush discharge shown on the pre- 



ceding page was doubtless a flash of the 

 latter character; and on the other hand, 

 with a kite in air during thunderstorms with a wire connection 

 to the ground I have experienced sharp shocks with lightning 



